A DIMM Riser Card With An Angled DIMM Socket And A Straddle Mount DIMM Socket

ABSTRACT

A DIMM riser card that includes a PCB having a first edge, a second edge, and one or more faces. The first edge of the PCB is configured for insertion into a main board DIMM socket. The first edge includes electrical traces that electrically couple to a memory bus. The DIMM riser card includes an angled DIMM socket mounted on one face of the PCB, where the angled DIMM socket is configured to accept a DIMM at an angle not perpendicular to the PCB and electrically couple the DIMM to the memory bus. The DIMM riser card includes a straddle mount DIMM socket mounted on the second edge of the PCB. The straddle mount DIMM socket is configured to accept a DIMM and electrically couple the DIMM to the memory bus through the electrical traces on the first edge of the PCB.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priorityfrom U.S. patent application Ser. No. 12/644,558, filed on Dec. 22,2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,Dual In-line Memory Module (‘DIMM’) riser cards, computer systemsconfigured with DIMM riser cards, and methods of manufacturing DIMMriser cards.

2. Description of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

Computer systems today increasingly require a greater amount of computermemory to operate. DIMM riser cards are utilized to extend the memorybus of a computer and increase the number of memory chips which may beinstalled in a computer mother board DIMM socket, without re-designingthe mother board. Current DIMM riser cards have several drawbackshowever. First, current DIMM riser cards have a large effective widthprohibiting many mother boards from utilizing the riser cards.Specifically, DIMM sockets on a typical motherboard are placed near oneother at a distance that less than the effective width of a riser card.As such, in many computer systems two riser cards cannot typically beplaced in adjacent DIMM sockets, limiting the usefulness of such risercards. Further, the current DIMM riser cards typically havesubstantially long electrical traces between upstream and downstreamsockets on the card. When the downstream socket is empty—containing noDIMM—the traces act as stub antennae and introduce stub effect intoelectrical signals transmitted along the memory bus.

SUMMARY OF THE INVENTION

Dual In-line Memory Module (‘DIMM’) riser cards, computer systemsconfigured with DIMM riser cards, and methods of manufacturing DIMMriser cards are disclosed. The DIMM riser cards include a printedcircuit board (‘PCB’) having a first edge, a second edge, and one ormore faces. The first edge of the PCB is configured for insertion into amain board DIMM socket mounted on a main board. The first edge alsoincludes electrical traces that electrically couple to a memory bus uponinsertion into the main board DIMM socket. The DIMM riser cards alsoinclude an angled DIMM socket mounted on one face of the PCB. The angledDIMM socket is configured to accept a DIMM at an angle not perpendicularto the PCB and electrically couple the DIMM to the memory bus throughthe electrical traces of the first edge. The DIMM riser cards alsoinclude a straddle mount DIMM socket mounted on the second edge of thePCB. The straddle mount DIMM socket is configured to accept a DIMM andelectrically couple the DIMM to the memory bus through the electricaltraces on the first edge of the PCB.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth a block diagram of automated computing machinerycomprising an exemplary computer having a DIMM riser card configuredaccording to embodiments of the present invention.

FIG. 2 sets forth a line drawing of a computer memory subsystem of theprior art.

FIG. 3 sets forth a line drawing of an exemplary computer memorysubsystem configured in accordance with embodiments of the presentinvention.

FIG. 4 sets forth a line drawing of an example DIMM riser cardconfigured in accordance with embodiments of the present invention.

FIG. 5 sets forth a flow chart illustrating an exemplary method formanufacturing a DIMM riser card according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary Dual In-line Memory Module (‘DIMM’) riser cards, computersystems configured with DIMM riser cards, and methods of manufacturingDIMM riser cards according to embodiments of the present invention aredescribed with reference to the accompanying drawings, beginning withFIG. 1. FIG. 1 sets forth a block diagram of automated computingmachinery comprising an exemplary computer (152) having a DIMM risercard configured according to embodiments of the present invention. Thecomputer (152) of FIG. 1 includes at least one computer processor (156)or ‘CPU’ as well as a random access memory (‘RAM’) (168) in a computermemory subsystem (138).

The RAM (168) in the example computer memory subsystem (138) of FIG. 1is implemented as a number of Double Data Rate Three (‘DDR3’)Synchronous dynamic RAM (‘SDRAM’) DIMMs. DDR3 SDRAM is a RAM interfacetechnology typically used for high bandwidth storage of the working dataof a computer or other digital electronic devices. DDR3 is part of theSDRAM family of technologies and is one of the many DRAMimplementations. DDR3 provides the ability to transfer at twice the datarate of DDR2, thus enabling higher bus rates and higher peak rates thanearlier memory technologies. In addition, the DDR3 standard allows forchip capacities of 512 megabits to 8 gigabits, effectively enabling amaximum memory module size of 16 gigabytes. A DIMM is a series of DRAMintegrated circuits. These circuits, called ‘modules,’ are mounted on aprinted circuit board and designed for use in personal computers,workstations and servers. The main difference between Single In-lineMemory Modules (‘SIMMs’) and DIMMs is that DIMMs have separateelectrical contacts on each side of the module, while the contacts onSIMMs on both sides are redundant. Another difference is that standardSIMMs have a 32-bit data path, while standard DIMMs have a 64-bit datapath. DDR3 SDRAM DIMMs are depicted in the example computer memorysubsystem (138) of FIG. 1 for clarity of explanation, not forlimitation. Readers of skill in the art will immediately recognize thatany DIMM type may be implemented in DIMM riser cards configured inaccordance with embodiments of the present invention.

The computer memory subsystem of FIG. 1 includes a memory controller(140) mounted on a main board. In the example of FIG. 1, the memorycontroller is implemented as part of a bus adapter (158). A memorycontroller is a digital circuit which manages the flow of data going toand from the main memory. It can be a separate chip or integrated intoanother chip, such as on the die of a microprocessor. A main board,sometimes called a motherboard, is a central PCB in many moderncomputers. A main board, for example, may hold many of the crucialcomponents of the system, while providing connectors for otherperipherals. A main board is sometimes alternatively known as a systemboard, a logic board, and sometimes shortened to mobo.

The computer memory subsystem (138) of FIG. 1 also includes a main boardDIMM socket (412). A DIMM socket as the term is used in thisspecification refers to a receptacle configured to receive a DIMM andelectrically couple the DIMM to a memory bus. A DIMM socket may beattached to a PCB using a through-hole technique, a surface mounttechnique, inserting pins of the DIMM socket into a connector, or inother ways as will occur to readers of a skill in the art. The ‘mainboard’ DIMM socket is a DIMM socket that connects DIMMs received in themain board DIMM socket to the memory bus of the main board.

The computer memory subsystem (138) of FIG. 1 also includes DIMM risercard (128) inserted into the main board DIMM socket (412). A riser cardis a PCB that picks up a number of signal lines, often bussed, via asingle connector, such as an edge connector on a main board anddistributes the signal lines via dedicated connectors on the card. Inthe example of FIG. 1, the DIMM riser card (128) includes a printedcircuit board (‘PCB’) having a first edge, a second edge, and one ormore faces. The first edge of the DIMM riser card is inserted into themain board DIMM socket (412). The first edge includes electrical tracesthat electrically couple to the memory bus through the main board DIMMsocket (412).

The DIMM riser card (128) in the example of FIG. 1 also includes anangled DIMM socket (418) mounted on one face of the PCB. The angled DIMMsocket (418) is configured to accept a DIMM (126) at an angle notperpendicular to the PCB. The angled DIMM socket (418) is alsoconfigured to electrically couple the DIMM (126) to the memory bus (166)through the electrical traces of the first edge of the DIMM riser cardPCB. The DIMM riser card (128) also includes a straddle mount DIMMsocket (404) mounted on the second edge of the PCB. The straddle mountDIMM socket (404) is configured to accept a DIMM (126) and electricallycouple the DIMM to the memory bus (166) through the electrical traces onthe first edge of the PCB of the DIMM riser card (128).

In some example embodiments, the computer memory subsystem (138) mayinclude a number of main board DIMM sockets and DIMM riser cards withangled and straddle mount sockets. In such an embodiment, the computersystem may have a greater memory density than a computer system havingriser cards without angled DIMM sockets. As explained in greater detailbelow with respect to FIGS. 2 and 3, DIMM riser cards with angled DIMMsockets may be located closer to one another than DIMM riser cardswithout angled DIMM sockets. As such, a computer system employing DIMMriser cards with angled DIMM sockets may have a greater memorydensity—more computer memory per unit of area—than a computer systemthat employs DIMM riser cards without angled DIMM sockets.

The computer memory subsystem (138) of FIG. 1 includes a memory bus(166) coupling the memory controller (140) and the main board DIMMsocket (412). That is, the DIMMs (126) of the computer memory subsystem(138) are connected through the main board DIMM socket (412), to thehigh speed memory bus (166) and bus adapter (158), to the processor(156), and to other components of the computer (152).

Stored in RAM (168) is a user level application (136), a module ofcomputer program instructions for carrying out user level dataprocessing tasks. Examples of user level applications include wordprocessor, spreadsheet applications, multimedia library applications,database management applications, image processing applications, and soon as will occur to readers of skill in the art. Also stored in RAM(168) is an operating system (154). Operating systems useful incomputers having DIMM riser cards configured in accordance withembodiments of the present invention include UNIX™ Linux™ Microsoft XP™AIX™, IBM's i5/OS™ and others as will occur to those of skill in theart. The operating system (154) and user level application (136) in theexample of FIG. 1 are shown in RAM (168), but many components of suchsoftware typically are stored in non-volatile memory also, such as, forexample, on a disk drive (170).

The computer (152) of FIG. 1 includes disk drive adapter (172) coupledthrough expansion bus (160) and bus adapter (158) to processor (156) andother components of the computer (152). Disk drive adapter (172)connects non-volatile data storage to the computer (152) in the form ofdisk drive (170). Disk drive adapters useful in computers that includeDIMM riser cards configured in accordance with embodiments of thepresent invention include Integrated Drive Electronics (‘IDE’) adapters,Small Computer System Interface (‘SCSI’) adapters, and others as willoccur to those of skill in the art. Non-volatile computer memory alsomay be implemented for as an optical disk drive, electrically erasableprogrammable read-only memory (so-called ‘EEPROM’ or ‘Flash’ memory),RAM drives, and so on, as will occur to those of skill in the art.

The example computer (152) of FIG. 1 includes one or more input/output(‘I/O’) adapters (178). I/O adapters implement user-orientedinput/output through, for example, software drivers and computerhardware for controlling output to display devices such as computerdisplay screens, as well as user input from user input devices (181)such as keyboards and mice. The example computer (152) of FIG. 1includes a video adapter (209), which is an example of an I/O adapterspecially designed for graphic output to a display device (180) such asa display screen or computer monitor. Video adapter (209) is connectedto processor (156) through a high speed video bus (164), bus adapter(158), and the front side bus (162), which is also a high speed bus.

The exemplary computer (152) of FIG. 1 includes a communications adapter(167) for data communications with other computers (182) and for datacommunications with a data communications network (100). Such datacommunications may be carried out serially through RS-232 connections,through external buses such as a Universal Serial Bus (‘USB’), throughdata communications networks such as IP data communications networks,and in other ways as will occur to those of skill in the art.Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a data communications network.Examples of communications adapters useful in computers having DIMMriser cards configured in accordance with embodiments of the presentinvention include modems for wired dial-up communications, Ethernet(IEEE 802.3) adapters for wired data communications networkcommunications, and 802.11 adapters for wireless data communicationsnetwork communications.

The arrangement of adapters, processors, networks, computers, and otherdevices making up the exemplary system illustrated in FIG. 1 are forexplanation, not for limitation. Data processing systems usefulaccording to various embodiments of the present invention may includeadditional servers, routers, other devices, and peer-to-peerarchitectures, not shown in FIG. 1, as will occur to those of skill inthe art. Networks in such data processing systems may support many datacommunications protocols, including for example TCP (TransmissionControl Protocol), IP (Internet Protocol), HTTP (HyperText TransferProtocol), WAP (Wireless Access Protocol), HDTP (Handheld DeviceTransport Protocol), and others as will occur to those of skill in theart. Various embodiments of the present invention may be implemented ona variety of hardware platforms in addition to those illustrated in FIG.1.

For further explanation, FIG. 2 sets forth a line drawing of a computermemory subsystem of the prior art. The prior art computer memorysubsystem of FIG. 2 includes two prior art riser cards (202, 204)connected to a main board (228) via main board sockets (232, 234). Priorart riser card (202) is configured with two DIMM sockets (206, 220) eachof which electrically couples a DIMM (210, 214) to one or more signallines on a PCB (224). Prior art riser card (204) is configured with twoDIMM sockets (208, 222) each of which electrically couples a DIMM (212,216) to one or more signal lines on a PCB (226). The sockets (206, 220,208, 222) are perpendicular to the PCB (224, 226) on which the socketsare mounted. The DIMMs are likewise installed in the sockets parallel toriser card in which the DIMM is installed and parallel to the mainboard. The distance (230) from the top of an installed DIMM (214) to theopposite face of the PCB (224) is greater than the height of the DIMMitself. As such, the riser cards (202, 204) must be spaced at a distancegreater than the distance (230) and greater from the top of an installedDIMM (214) to the opposite face of the PCB (224)—effectively greaterthan the height of a DIMM.

For further explanation, FIG. 3 sets forth a line drawing of anexemplary computer memory subsystem configured in accordance withembodiments of the present invention. FIG. 3 differs from FIG. 2 in thatthe example computer memory subsystem of FIG. 3 includes three risercards (302, 304, 306) with each riser card including a PCB (332, 334,336) having a first edge, a second edge, and one or more faces. Thefirst edge is inserted into a main board DIMM socket (338, 340, 342)mounted on a main board (344). The first edge includes electrical tracesthat electrically couple to a memory bus upon insertion into the mainboard DIMM socket (338, 340, 342).

Each of the DIMM riser cards (302, 304, 306) includes an angled DIMMsocket (320, 322, 324) mounted on one face of the PCB (332, 334, 336).The angled DIMM socket (320, 322, 324) accepts a DIMM (326, 328, 330) atan angle not perpendicular to the PCB. In the example of FIG. 3, DIMM(326) and DIMM (328) are directed at angle pointing toward the mainboard (344) while DIMM (330) is directed at an angle point away from themain board (344). That is, DIMM riser cards configured in accordancewith embodiments of the present invention may include angled DIMM socketthat accept a DIMM at an angle that directs the DIMM toward the firstedge of the PCB or that accept a DIMM at an angle that directs the DIMMtoward the second edge of the PCB. Each angled DIMM socket (320, 322,324) is also configured to electrically couple the DIMM (326, 328, 330)to the memory bus through the electrical traces of the first edge of thePCB (332, 334, 336).

Each of the DIMM riser cards (302, 304, 306) also includes a straddlemount DIMM socket (314, 316, 318) mounted on the second edge of the PCB(332, 334, 336). The term ‘straddle mount’ describes the type ofmounting of the DIMM socket—by straddling pins from the bottom of thestraddle mount DIMM socket over the second edge of the riser card. Thepins of the straddle mount DIMM socket may insert into through holes, besoldered onto pads or electrical traces on the PCB, or may otherwise beelectrically coupled to the electrical traces of the PCB. The straddlemount DIMM sockets (314, 316, 318) accept a DIMM (308, 310, 312) andelectrically couple the DIMM (308, 310, 312) to the memory bus throughthe electrical traces on the first edge of the PCB.

The example computer memory subsystem of FIG. 3 also differs from theprior art subsystem of FIG. 2 in that the distance (346) from the top ofa DIMM (328) installed in an angled DIMM socket (322) to the oppositeface of the PCB (334) is less than the distance (230 on FIG. 2) from thetop of a DIMM (214 on FIG. 2) installed in a perpendicular DIMM socket(220 on FIG. 2) to the opposite face of the PCB (224 on FIG. 2). Thatis, the effective width of a DIMM riser card having a DIMM installed inan angled DIMM socket is less than the effective width of a DIMM risercard having a DIMM installed in perpendicular DIMM socket. As such, DIMMriser cards having an angled DIMM socket may be configured physicallycloser to one another than DIMM riser cards having perpendicular DIMMsockets. A computer memory subsystem including DIMM riser cards withangled DIMM sockets may be configured with a greater memorydensity—number of DIMM riser cards per unit of area—than a computermemory subsystem that includes DIMM riser cards without angled DIMMsockets.

For further explanation, FIG. 4 sets forth a line drawing of an exampleDIMM riser card (402) configured in accordance with embodiments of thepresent invention. The example DIMM riser card (402) of FIG. 4 includesa PCB (426). The PCB (426) has a first edge (414), a second edge (422),and one or more faces (410). The first edge (414) is inserted into amain board DIMM socket (412) mounted on a main board (416). The firstedge (414) includes electrical traces that electrically couple to amemory bus (420) upon insertion into the main board DIMM socket (414).

The example DIMM riser card (402) of FIG. 4 also includes an angled DIMMsocket (418) mounted on one face (410) of the PCB (426). The angled DIMMsocket (418) is configured to accept a DIMM (408) at an angle notperpendicular to the PCB. The angled DIMM socket (418) is alsoconfigured to electrically couple the DIMM (408) to the memory bus (420)through the electrical traces of the first edge (414).

The example DIMM riser card (402) of FIG. 4 also includes a straddlemount DIMM socket (404) mounted on the second edge (422) of the PCB(426). The straddle mount DIMM socket (404) is configured to accept aDIMM (409) and electrically couple the DIMM (409) to the memory bus(420) through the electrical traces on the first edge (414) of the PCB(426).

In the example DIMM riser card (402) of FIG. 4, the angled DIMM socket(418) and the straddle mount DIMM socket (404) are located adjacent toone another on the PCB such that stub effect induced by electricaltraces (406) between the angled DIMM socket (418) and the straddle mountDIMM (404) is reduced when no DIMM is installed in the straddle mountDIMM socket (404). The electrical traces (406) electrically couple thedownstream straddle mount DIMM socket to the upstream Angled DIMM socketwhich is electrically coupled through the traces on the first edge (414)of the PCB (426) and through the main board DIMM socket (412) to thememory bus (420). When no DIMM is installed in the straddle mount DIMMsocket (404), the traces (406) between the angled DIMM socket (418) andthe straddle mount DIMM socket (404) may function as stub antennas andintroduce interference, called stub effect, into electrical signalscarried on the traces of the PCB. Stub effect may be reduced by reducingthe length of the traces. In the example DIMM riser card (402) of FIG.4, the length of the traces is reduced by physically locating the angledDIMM socket (418) near the straddle mount DIMM socket.

The example DIMM riser card (402) of FIG. 4, also includes a chip selectconnector (424) electrically coupled to one or more DIMMs installed onthe DIMM riser card. A chip select signal, also called slave select, isthe name of a control line in digital electronics used to select onechip out of several connected to the same computer bus usually utilizingthe three-state logic. For DIMMs, the chip select may be used to selecta set of memory modules on the DIMM to write to or read from. Theexample chip select connector (424) of FIG. 4 is capable of receiving achip select cable that couples one or more chip select signal lines ofthe main board (416) to a DIMM (408, 409) installed on the DIMM risercard (402). The example straddle mount DIMM socket (404) and the angledDIMM socket (418) of the DIMM riser card (402) of FIG. 4 may beconfigured to accept a dual die, quad rank, two DIMM per channel, doubledata rate three (DDR3) DIMM.

For further explanation, FIG. 5 sets forth a flow chart illustrating anexemplary method for manufacturing a DIMM riser card according toembodiments of the present invention. The method of FIG. 5 includesconfiguring (502) a PCB having a first edge, a second edge, and one ormore faces for insertion into a main board

DIMM socket mounted on a main board. In the method of FIG. 5,configuring (502) a PCB for insertion into a main board DIMM socketincludes etching electrical traces along the first edge thatelectrically couple to a memory bus upon insertion into the main boardDIMM socket.

The method of FIG. 5 also includes mounting (506) to the second edge ofthe PCB a straddle mount DIMM socket. In the method of FIG. 5, thestraddle mount DIMM socket is configured to accept a DIMM andelectrically couple the DIMM to the memory bus through the electricaltraces on the first edge of the PCB. Mounting (506) the straddle mountDIMM socket to the second edge of the PCB may be carried out in variousways including soldering the pins of the straddle mount DIMM socket topads on opposite faces of the PCB of the DIMM riser card, where the padsare located near the second edge of the PCB of the DIMM riser card.

The method of FIG. 5 also includes mounting (504) on one face of the PCBan angled DIMM socket. In the method of FIG. 5, the angled DIMM socketis configured to accept a DIMM at an angle not perpendicular to the PCB.The angled DIMM socket electrically couples the DIMM to the memory busthrough the electrical traces of the first edge of the PCB. Mounting(504) the angled DIMM socket on one face of the PCB may be carried outin various ways including, for example, inserting pins of the angledDIMM socket through through-holes on the PCB and soldering the pins tothe through-holes, soldering pads of the DIMM socket to pads of the PCB,and in other ways as will occur to readers of skill in the art. In themethod of FIG. 5, mounting (504) the angled DIMM socket on one face ofthe PCB includes mounting (510) the angled DIMM socket adjacent to thestraddle mount DIMM socket to reduce stub effect induced by electricaltraces between the angled DIMM socket and the straddle mount DIMM whenno DIMM is installed in the straddle mount DIMM socket.

In the method of FIG. 5, mounting (504) the angled DIMM socket mayinclude mounting (512) the angled DIMM socket to accept a DIMM at anangle that directs the DIMM toward the first edge of the PCB or mounting(514) the angled DIMM socket to accept a DIMM at an angle that directsthe DIMM toward the second edge of the PCB. The angled DIMM socket mayaccept a DIMM at an angle such that a distance from the top of the DIMMto an opposite face of the DIMM riser card is greater than a distancefrom a top of a DIMM installed in a non-angled socket to an oppositeface of a DIMM riser card.

The method of FIG. 5 also includes mounting (508) to the PCB a chipselect connector. In the method of FIG. 5, the mounted chip selectconnector electrically couples to one or more DIMMs installed on theDIMM riser card. T chip select connector is also capable of receiving achip select cable where the chip select cable couples one or more chipselect signal lines of the main board to a DIMM installed on the DIMMriser card.

In view of the explanations set forth above, readers will recognize thatthe benefits of DIMM riser cards having an angled DIMM socket and astraddle mount DIMM socket according to embodiments of the presentinvention include:

-   -   Greater memory density in computer memory subsystems; and    -   A reduced amount of stub effect when a DIMM is not installed in        a downstream DIMM socket.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

1. A Dual In-line Memory Module (‘DIMM’) riser card, the DIMM riser cardcomprising: a printed circuit board (‘PCB’) having a first edge, asecond edge, and one or more faces, the first edge configured forinsertion into a main board DIMM socket mounted on a main board; anangled DIMM socket mounted on one face of the PCB, the angled DIMMsocket configured to accept a DIMM at an angle not perpendicular to thePCB; and a straddle mount DIMM socket mounted on the second edge of thePCB, the straddle mount DIMM socket configured to accept a DIMM.
 2. TheDIMM riser card of claim 1 wherein a distance from a top of a DIMMinstalled in the angled socket to an opposite face of the DIMM risercard is greater than a distance from a top of a DIMM installed in anon-angled socket to an opposite face of the DIMM riser card.
 3. TheDIMM riser card of claim 1 wherein the angled DIMM socket and thestraddle mount DIMM socket are located adjacent to one another such thatstub effect induced by electrical traces between the angled DIMM socketand the straddle mount DIMM is reduced when no DIMM is installed in thestraddle mount DIMM socket.
 4. The DIMM riser card of claim 1 furthercomprising a chip select connector electrically coupled to one or moreDIMMs installed on the DIMM riser card, the chip select connectorcapable of receiving a chip select cable, the chip select cable couplingone or more chip select signal lines of the main board to a DIMMinstalled on the DIMM riser card.
 5. The DIMM riser card of claim 1wherein the angled DIMM socket is further configured to accept a DIMM atan angle that directs the DIMM toward the first edge of the PCB.
 6. TheDIMM riser card of claim 1 wherein the angled DIMM socket is furtherconfigured to accept a DIMM at an angle that directs the DIMM toward thesecond edge of the PCB.
 7. The DIMM riser card of claim 1 wherein thestraddle mount DIMM socket and the angled DIMM socket are configured toaccept a dual die, quad rank, two DIMM per channel, double data ratethree (DDR3) DIMM.
 8. A computer comprising: a computer processor; acomputer memory subsystem operatively electrically coupled to thecomputer processor, wherein the computer memory subsystem furthercomprises: a memory controller mounted on a main board; a main boardDIMM socket; a memory bus coupling the memory controller and the mainboard DIMM socket; and a DIMM riser card inserted into the main boardDIMM socket, wherein the DIMM riser card further comprises: a printedcircuit board (‘PCB’) having a first edge, a second edge, and one ormore faces, the first edge inserted into the main board DIMM socket; anangled DIMM socket mounted on one face of the PCB, the angled DIMMsocket configured to accept a DIMM at an angle not perpendicular to thePCB; and a straddle mount DIMM socket mounted on the second edge of thePCB, the straddle mount DIMM socket configured to accept a DIMM.
 9. Thecomputer of claim 8 further comprising a plurality of main board DIMMsockets, each main board DIMM socket coupling a DIMM riser card havingan angled DIMM socket and a straddle mount DIMM socket to the memorybus, wherein the computer comprises a greater memory density than acomputer having riser cards without angled DIMM sockets.
 10. Thecomputer of claim 8 wherein the angled DIMM socket and the straddlemount DIMM socket are located adjacent to one another such that stubeffect induced by electrical traces between the angled DIMM socket andthe straddle mount DIMM is reduced when no DIMM is installed in thestraddle mount DIMM socket.
 11. The computer of claim 8 wherein the DIMMriser card further comprises a chip select connector electricallycoupled to one or more DIMMs installed on the DIMM riser card, the chipselect connector capable of receiving a chip select cable, the chipselect cable coupling one or more chip select signal lines of the mainboard to a DIMM installed on the DIMM riser card.
 12. The computer ofclaim 8 wherein the angled DIMM socket is further configured to accept aDIMM at an angle that directs the DIMM toward the first edge of the PCB.13. The computer of claim 8 wherein the angled DIMM socket is furtherconfigured to accept a DIMM at an angle that directs the DIMM toward thesecond edge of the PCB.
 14. The computer of claim 8 wherein the straddlemount DIMM socket and the angled DIMM socket are configured to accept adual die, quad rank, two DIMM per channel, double data rate three (DDR3)DIMM.
 15. A method of manufacturing a Dual In-line Memory Module(‘DIMM’) riser card, the method comprising: configuring a printedcircuit board (‘PCB’) having a first edge, a second edge, and one ormore faces for insertion into a main board DIMM socket mounted on a mainboard; mounting on one face of the PCB an angled DIMM socket, the angledDIMM socket configured to accept a DIMM at an angle not perpendicular tothe PCB; and mounting to the second edge of the PCB a straddle mountDIMM socket, the straddle mount DIMM socket configured to accept a DIMM.16. The method of claim 15 wherein a distance from a top of a DIMMinstalled in the angled socket to an opposite face of the DIMM risercard is greater than a distance from a top of a DIMM installed in anon-angled socket to an opposite face of a DIMM riser card.
 17. Themethod of claim 15 wherein mounting the angled DIMM socket furthercomprises mounting the angled DIMM socket adjacent to the straddle mountDIMM socket to reduce stub effect induced by electrical traces betweenthe angled DIMM socket and the straddle mount DIMM when no DIMM isinstalled in the straddle mount DIMM socket.
 18. The method of claim 15further comprising mounting to the PCB a chip select connector, themounted chip select connector electrically coupled to one or more DIMMsinstalled on the DIMM riser card, the chip select connector capable ofreceiving a chip select cable, the chip select cable coupling one ormore chip select signal lines of the main board to a DIMM installed onthe DIMM riser card.
 19. The method of claim 15 wherein mounting theangled DIMM socket further comprises mounting the angled DIMM socket toaccept a DIMM at an angle that directs the DIMM toward the first edge ofthe PCB.
 20. The method of claim 15 wherein mounting the angled DIMMsocket further comprises mounting the angled DIMM socket to accept aDIMM at an angle that directs the DIMM toward the second edge of thePCB.